Tuberization in Potato at High Temperatures: interaction between Shoot and Root Temperatures

Tuber formation in intact potato plants (Solanum tuberosum L.cv. Sebago) was reduced by high shoot or root temperatures andstrongly inhibited when both were high. When both the shootand root temperatures were high, disbudding strongly promotedtuberization. There was a smaller increase with warm roots andcool shoots, but no response with warm shoots and cool roots.When both the shoots and roots were cool, disbudding reducedtuberization. Exogenous GA₃, effectively substituted for thebuds at high temperatures, completely preventing tuberization.In apical cuttings, removal of the terminal bud, but not theroots, reduced the inhibitory effects of high temperatures ontuberization. The experiment indicates that tuber productionmay be controlled by at least three factors: a promoter, whichis not assimilate, produced by the buds at cool temperatures;an inhibitor, derived from the buds, but dependent on warm roottemperatures for its formation; and a second inhibitor derivedfrom the mature leaves and produced in response to warm shoottemperatures. Solanum tuberosumL, potato, tuberization, temperature, disbudding, gibberellic acid     

Tuberization in Potato at High Temperatures: Promotion by Disbudding

The role of the terminal and axillary buds, as presumptive organsof gibberellin synthesis, in the control of tuberization inpotato (Solanum tuberosum L., cv. Sebago) at high temperatureswas studied. Decapitation alone strongly promoted the outgrowthof axillary buds, but did not promote tubenzation. When growthof the axillary buds was suppressed by the use of chemical pruningagents (MH, TIBA or 1-decanol), tuberization was promoted. Manualremoval of the buds promoted tuberization to a similar extent.The results are consistent with the hypothesis that the budsare major sites of gibberellin synthesis in the potato, andthat high temperatures stimulate the synthesis of gibberellinsand their export to the stolons, where they inhibit tuber formation. Solarium tuberosum L., potato, tuberization, temperature, disbudding, chemical pruning, gibberellins     

Tuberization in Potato at High Temperatures: Gibberellin Content and Transport from Buds

Warm temperatures (35°C day/30°C night) which inhibittuberization in potato (Solanum tuberosum L., cv. Sebago) increasedgibberellin activity in crude extracts from buds, but not frommature leaves, as determined by the lettuce hypocotyl bioassay.Changes in the growth of tubers and stolons indicate the occurrenceof basipetal movement of GA₃ applied to the terminal bud ora mature leaf. ¹⁴C labelling from GA₃ or mevalonic acid injectedjust below the terminal bud was recovered in the lower shoot,stolons and tubers, but the amount transported was greater atcool temperatures (20/15°C). It is concluded that high temperaturespromote the synthesis of gibberellin in the buds rather thantransport to the stolons. Solanum tuberosum L., potato, tuberization, gibberellin     

Tuberization in Potato at High Temperatures: Responses to Gibberellin and Growth inhibitors

The responses of potato plants (Solanum tuberosum L., cv. Sebago)to high temperatures (32 day/28 C night or 32/18 °C) andgibberellin are similar, in that they promote haulm growth andsuppress tuber production, whereas low temperatures (22/18 °C)abscisic acid and CCC have the opposite effect, promoting tuberproduction and reducing the growth of the haulms. The inhibitoryeffect of the high temperatures on tuber production, under aphotoperiod of 14 h, was almost completely reversed in theseexperiments by the application of CCC, and partly reversed byABA. Single-leaf cuttings from plants grown at the various temperaturesand chemical treatments responded in the same way as the wholeplant. It is suggested that both haulm growth and tuber initiationare influenced by a common hormonal control, and that temperatureexerts its influence by altering the balance between the levelsof endogenous gibberellins and inhibitors. These substancesapparently act directly on the stolon tip, rather than throughtheir general influence on haulm growth. Solanum tuberosum L., potato, tuberization, temperature response, gibberellin, abscisic acid, 2-chloroethyltrimethylammonium chloride (CCC)     

The Interaction of Gibberellins and Photoperiod in the Control of Potato Tuberization

Solanum tuberosum ssp. andigena plants require a short-day (SD) photoperiod for tuber formation, a process that is also affected by gibberellins (GAs). Grafting experiments have confirmed that the photoperiod is perceived in the leaves. Tuber formation, however, usually takes place in the underground stolons. In this review, photoperiod-dependent tuberization has been divided into five chronological events: SD photoperiod perception, short-term adaptive responses to SD conditions, generation and transport of tuber-inducing signal(s), tuber formation, and long-term adaptive responses to tuber growth. Within this frame of study, the interaction of GAs and photoperiod is revised. Similar to the flowering process in Arabidopsis, we suggest the existence of two independent pathways that control tuber formation: a photoperiod-dependent pathway and a GA-dependent pathway. Nevertheless, photoperiod-dependent tuber formation requires the action of GAs at specific stages to orchestrate this complex process of development.     

The Effect of High Temperatures on the Photosynthetic Activity of Intact Barley Leaves at Low and High Irradiance

Light curves of CO₂ fixation by barley seedling leaves preliminarily heated at 30–43°C for 5 min were measured. The slope of the linear part of the light curve decreased after leaf heating at temperatures above 35°C; whereas, at a high light level, the photosynthesis rate decreased only at temperatures of 40°C and higher. The linear relationships between the photosynthetic CO₂-fixation rate and a photon flux density up to 1400 mol/(m² s) were found in leaves preheated at 42°C; this indicates the strong nonphotochemical dissipation of absorbed light quanta. The lowering of the oxygen concentration from 21 to 1% led to a CO₂ fixation maximum quantum yield and a photosynthesis-rate increase at the highest light intensity in leaves preheated at temperatures above 40°C as compared to the control leaves. Nevertheless, the linear relationship between the photosynthetic CO₂ fixation and the light intensity was found in leaves heated at 42°C at O₂ concentrations of both 21 and 1%. The latter fact suggests that the proton gradient of the thylakoid membrane, which causes an increase in the nonphotochemical dissipation of the quanta absorbed, could also be formed due to the cyclic electron transport over photosystem I.     

Effects of High Air and Soil Temperature Stress on Growth and Tuberization in Solanum tuberosum

Potato plants (Solanum tuberosum L.) were grown at differentair and soil temperatures to determine the effects of high-temperaturestress on root, tuber, and shoot growth. Cooling the soil (17–27C) at high air temperatures (30–40 C) relieved noneof the visible symptoms of heat stress on shoot growth; norwas the degree of induction to tuberize in leaves increased,as reflected in tuberization of leaf-bud cuttings. Heating thesoil (27–35 C) at cool (17–27 C) air temperatureshad no apparent detrimental effect on shoot growth or inductionof leaves to tuberize. However, in each case hot soil largelyeliminated tuber development. In one experiment stolons grewup out of the hot soil and formed aerial tubers upon reachingthe cool air. When leaf-bud cuttings from induced plants wereused as a model system, high soil temperatures inhibited tuberdevelopment from the buried leaf buds, in the absence of anyroot growth. Apparently the induction of leaves to tuberizeis affected principally by air rather than soil temperature,but expression of the signal to tuberize can be blocked by highsoil temperature. Solanum tuberosum L., potato, temperature stress, soil temperature, tuberization     

Blue Light Inhibition of Tuberization in a Day-Neutral Potato

In tests on the effects of light quality on potato tuberization, continuous blue light was found to consistently inhibit tuberization of tissue-cultured plantlets of Solanum tuberosum ssp. tuberosum cv. ??Norland??. Other tested cultivars, including sports of ??Norland??, formed tubers under continuous blue light. Microarrays identified BL, GA7ox, and Nudix genes as exhibiting altered expression in response to blue light treatment. Quantitative RT-PCR (qRT-PCR) showed that GA7ox RNA increased in ??Norland?? but not in ??Sangre?? plantlets in blue light compared to darkness. RNA levels of genes identified in the literature as having roles in potato tuberization were also measured using qRT-PCR. Levels of GA20o1x, but not GA2ox, RNA increased in response to blue light in ??Norland?? plantlets. BEL5 RNA content was greater under blue light compared to darkness for both ??Norland?? and ??Sangre?? plants. Levels of FT were not significantly different in blue light compared to dark-treated ??Norland?? plants, but were low in blue light-treated compared to dark-treated ??Sangre?? plants. Addition of ancymidol to ??Norland?? plants exposed to blue light overcame blue light inhibition of tuberization. Ancymidol prevents the oxidation of ent-kaurene to ent-kaurenoic acid, thus inhibiting gibberellin biosynthesis. These data suggest that blue light may increase GA accumulation in ??Norland?? plants, as has been shown to occur in Arabidopsis plants. The novel effect of blue light in inhibiting tuberization of ??Norland?? plants suggests that this system could be a useful tool in further elucidating the mechanisms of day-neutral potato tuberization.     

Theobroxide Triggers Jasmonic Acid Production to Induce Potato Tuberization in vitro

Theobroxide, a novel compound isolated from fungus Lasiodiplodia theobromae culture, stimulates potato (Solanum tuberosum L.) tuber formation in vitro and in vivo, and induces flowering of Japanese morning glory (Pharbitis nil) under non-inductive long day conditions. To assess the mode of action of theobroxide in the tuberization process we measured endogenous levels of jasmonic acid and lipoxygenase activity in the cultures after the treatment with theobroxide. The results showed that theobroxide not only stimulated microtuber formation alone, but also enhanced the inductive effect of jasmonic acid when they were used in combination. The endogenous JA content increased in response to theobroxide in both old and new tissues. Moreover, theobroxide increased lipoxygenase activity in the cultures, at 2 and 3 week after culture initiation. Additionally, histological observations indicated that theobroxide might play a role in the swelling of micro-tubers formed in vitro in a similar manner as that of jasmonic acid. These results suggest that the inductive effect of theobroxide on potato micro-tuber formation might be achieved through triggering jasmonic acid production.     

Changes in Calcium-Dependent Protein Kinase Activity during in Vitro Tuberization in Potato

A soluble Ca2+-dependent protein kinase (CDPK) was purified to homogeneity in potato (Solanum tuberosum L.) plants. Potato CDPK was strictly dependent on Ca2+ (one-half maximal activation 0.6 [mu]M) and phosphorylated a wide diversity of substrates, in which Syntide 2 was the best phosphate acceptor (Michaelis constant = 30 [mu]M). The kinase was inhibited by Ca2+-chelating agents, phenotiazine derivatives, and N-(6-aminohexyl)-5-chloro-1-naphthalenesulfonamide (one-half maximal inhibition = 0.25 mM). Polyclonal antibodies directed against the regulatory region of the soybean CDPK recognized a 53-kD polypeptide. In an autophosphorylation assay, this same band was strongly labeled with [[gamma]-32P]ATP in the presence of Ca2+. CDPK activity was high in nontuberized plants, but increased 2.5-fold at the onset of tuber development and was reduced to one-half of its original activity when the tuber had completed formation. In the early stages of tuberization, Ca2+-dependent phosphorylation of endogenous targets (specific bands of 68, 51, and 46 kD) was observed. These polypeptides were not labeled in nontuberizing plants or in completely formed tubers, indicating that this phosphorylation is a stage-specific event. In addition, dephosphorylation of specific polypeptides was detected in tuberizing plants, suggesting the involvement of a phosphatase. Preincubation of crude extracts with phosphatase inhibitors rendered a 100% increase in CDPK activity.     

Contrasting Changes of Photosystem 2 Efficiency in Arabidopsis Xanthophyll Mutants at Room or Low Temperature Under High Irradiance Stress

We compared the responses of wild type (WT) and three mutants including npq1 (lutein-replete and violaxanthin deepoxidase-deficient), lut2 (lutein-deficient), and lut2-npq1 (double mutant) to high irradiance (HI, 2 000 μmol m⁻² s⁻¹) at both low (LT, 5 °C) and room (25 °C) temperature. Xanthophyll-dependent energy dissipation was highest in the WT, followed by the lut2, npq1, and npq1-lut2. At 25 °C the relative stress tolerance expressed by F_v/F_m was consistent with the energy dissipation capacity for the first 2 h of treatment. After 3–4 h, the F_v/F_m levels in lut2 and npq1 converged. Under combined LT and HI the relative tolerance sequence was in contrast to the energy dissipation capacity being WT > npq1> lut2 > lut2-npq1. There were little or no significant change in the contents of xanthophylls and carotenes or the chlorophyll (Chl) a/b ratio in any of the materials. Thus lutein (L) substitution possibly alters the conformation/organisation of L binding proteins to enhance damage susceptibility under HI at LT. The enhanced vulnerability is not compensated for the energy dissipation capacity in the lut2 background at LT. This revised version was published online in August 2006 with corrections to the Cover Date.     

Biological and Abiological Sulfur Reduction at High Temperatures

Reduction of elemental sulfur was studied in the presence and absencè of thermophilic sulfur-reducing bacteria, at temperatures ranging from 65 to 110°C, in anoxic artificial seawater media. Above 80°C, significant amounts of sulfide were produced abiologically at linear rates, presumably by the disproportionation of sulfur. These rates increased with increasing temperature and pH and were enhanced by yeast extract. In the same medium, the sulfur respiration of two recent thermophilic isolates, a eubacterium and an archaebacterium, resulted in sulfide production at exponential rates. Although not essential for growth, sulfur increased the cell yield in both strains up to fourfold. It is suggested that sulfur respiration is favored at high temperatures and that this process is not limited to archaebacteria, but is shared by other extreme thermophiles.     

光周期调节马铃薯块茎形成的分子机制

光周期调节马铃薯块茎形成的分子机制研究最近取得了很大进展.综合介绍了赤霉素(gibberellins,GAs)、马铃薯StCOL3(CONSTANS-LIKE3)基因和StFT(FLOWERING LOCUST)基因以及蔗糖运输载体(sucrose transporters,SUTs)在短日照调节马铃薯块茎形成中的作用.     

Physiology of Tuberization in Solanum tuberosum L: cis-Zeatin Riboside in the Potato Plant: Its Identification and Changes in Endogenous Levels as Influenced by Temperature and Photoperiod

Using high pressure liquid chromatography, the cucumber cotyledon bioassay, and mass spectrometry a cytokinin isolated from Solanum tuberosum L. cv. Katahdin plant tissues has been identified as cis-zeatin riboside. Zeatin riboside (ZR) levels in plants grown under inducing conditions (28 C day and 13 C night with a 10-hour photoperiod) were significantly higher than those in plants grown under noninducing conditions (30 C day and 28 C night with an 18-hour photoperiod). The highest level of ZR was noted in below-ground tissue after 4 days exposure to inducing conditions, with tuber initiation observed after 8 days. A companion study conducted to determine the effect of ZR on in vitro tuberization of noninduced rhizomes revealed that after 1 month in culture, controls exhibited 0% tuberization, while ZR treatments of 0.3 and 3.0 milligrams per liter showed 39 and 75% tuberization, respectively.     

Effect of Calcium on Tuberization in Potato (Solanum tuberosum L.)

Tuberization response of single-node leaf cuttings from induced potato plants (Solanum tuberosum L.) was reversed when pretreated with 5 millimolar ethyleneglycol-bis-(beta-aminoethyl ether)N,N'-tetraacetic acid (EGTA) + 50 micromolar calcium ionophore (A23187) and resumed when transferred to a CaCl(2)-containing medium. Tuberization was inhibited by LaCl(3), chlorpromazine, and trifluoperazine at 5 to 10 micromolar. These results suggest a role for calcium in the tuberization process.